"We have a squid-centric view of life from my lab," the Woods Hole Oceanographic Institution scientist said. Mooney partly focuses on squids because of the important role they play in ocean ecology.

"We view squid as this organism that either eats or is eaten by everything in the ocean at some point," he said. "When squid populations change, it often impacts other animals such as albatross egg production or fisheries production."

The squid Mooney studies, Atlantic longfin squid, is also fished and sold as calamari, and is an important food source for other market fish, like haddock and cod.

The researcher is particularly interested in squids' inner ear bones, which are called statoliths. That's because squids use these statoliths for important functions, like balancing and directing themselves as they jet around the ocean.

Recent work published by Mooney and his graduate student Max Kaplan shows ocean acidification, caused by increasing levels of carbon dioxide being absorbed by the ocean, may have a negative effect on those statoliths and on squids themselves.

In a study published Friday in the journal PLOS ONE, Mooney and Kaplan reported on their experiments hatching Atlantic longfin squid in both regular ocean water and acidified ocean water, mimicking the conditions likely to be seen in the oceans in 100 years.

The squid eggs placed in the acidified water hatched later, were smaller and had what the paper calls "irregular" statoliths.

Statoliths are made out of a form of calcium carbonate called aragonite. Because they are inside the squid, Mooney and his fellow researchers were unsure whether they would be affected by the acidified ocean.

Acidity may impair movement
Previous research has shown that when carbon dioxide is absorbed by the ocean and it becomes more acidic, concentrations of calcium carbonate drop, and that hurts shellfish and corals, which use calcium carbonate to build shells and skeletons.

What they found, though, was that the statoliths of squids raised in the acidified tank were smaller, more porous and less dense, and the tiny crystals that make up the statolith were organized more irregularly than those in a normal squid.

Mooney thinks this could affect the squids' ability to swim. That's one of the next experiments he and Kaplan plan to run.

"We'll basically put a bunch [of the squids] in a fish tank and then track three-dimensional movement," he said. His hunch is that squids with irregular statoliths might not be able to swim straight and could be slower.

In the wild, these effects could determine whether a squid lives or dies.

Squid larvae that take longer to hatch, as the ones in the acidified tank did, are available to predators longer. If squids are smaller, they can't swim as quickly, and if they can't control their movements as well, they are also more vulnerable.

Iliana Ruiz-Cooley, a scientist at the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center who is familiar with Mooney’s research, agreed it is important to further investigate how acidification might affect statoliths in squid.

If their movement is negatively affected, this could hurt their ability to avoid predators and also their ability to capture prey, she said.

This research provides an important baseline for future studies on squid, which, Ruiz-Cooley said, are challenging to research.

“Squid are a highly dynamic species … it is difficult to investigate them in the wild,” said Ruiz-Cooley.

As Mooney acknowledged, this first study did expose the squids to fairly extreme acidified conditions, ones unlikely to be present in the ocean for quite a while.

That's because this was a preliminary study primarily to see whether ocean acidification had an effect.

Now that they know it did, the researchers will do a "dose-response" set of experiments, setting squid larvae in tanks with varying concentrations of dissolved CO2 to see what happens, Mooney said.

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